The e-mails were obtained by an FBI-led task force in San Diego between late last year and June but were not forwarded to the military, according to government and congressional sources. Some were sent to the FBI's Washington field office, triggering an assessment into whether they raised national security concerns, but those intercepted later were not, the sources said.
Hasan's contacts with extremist imam Anwar al-Aulaqi began as religious queries but took on a more specific and concrete tone before he moved to Texas, where he allegedly unleashed the Nov. 5 attack that killed 13 people and wounded nearly three dozen, said the sources who were briefed on the e-mails, speaking on the condition of anonymity because the case is sensitive and unfolding. One of those sources said the two discussed in "cryptic and coded exchanges" the transfer of money overseas in ways that would not attract law enforcement attention.
"He [Hasan] clearly became more radicalized toward the end, and was having discussions related to the transfer of money and finances . . .," said the source, who spoke at length in part because he was concerned the public accounting of the events has been incomplete. "It became very clear toward the end of those e-mails he was interested in taking action."
Senate Armed Services Committee Chairman Carl M. Levin (D-Mich.) said Friday that he would investigate the handling of the e-mails -- 18 or 19 in all -- and why military officials were not aware of them before the deadly attack. Levin told reporters after a briefing from Pentagon staff members that "there are some who are reluctant to call it terrorism, but there is significant evidence that it is."
Bits and pieces of Hasan's communications with Aulaqi have become public since the Fort Hood massacre, but the sources provided the most detailed description yet of the messages. The e-mails will help investigators determine whether Hasan's alleged actions were motivated by psychological deterioration or inspired by radical religious views he found online and through e-mail exchanges with Aulaqi.
The sources said the e-mail correspondence is particularly troubling because Aulaqi, who has been on the law enforcement radar for years, is considered by U.S. officials to be an al-Qaeda supporter who has inspired terrorism suspects in Britain, Canada and the United States. Lawmakers and counterterrorism experts have questioned why no one in the government interceded earlier given Aulaqi's history and Hasan's military position.
The disclosures came as investigators in the FBI and the Army's Criminal Investigation Division continue to interview witnesses and execute search warrants in and around the Army's largest post, in Killeen, Tex., and elsewhere.
This week Defense Secretary Robert M. Gates launched a department-wide review to determine whether military procedures hinder the identification of service members who pose a threat to their fellow troops.
Hasan faces 13 charges of premeditated murder. He is scheduled to have his first formal court hearing Saturday, in his hospital room in the intensive care unit at the Brooke Army Medical Center in San Antonio, where he is recovering from gunshot wounds that have left him paralyzed.
Hasan's contacts with Aulaqi were not publicly disclosed until after the shootings, which the cleric subsequently praised, calling the Army psychiatrist a "hero" in a posting on his Web site.
In the months before the shootings, the two discussed how Hasan could make several transactions of less than $10,000, a threshold for reporting to U.S. authorities, according to the source who spoke extensively. Hasan did not explicitly vow to fund terrorist activities or evade tax and reporting laws for contributions, the source said.
"I believe they were interested in the money for operational-type aspects, and knowing that he had funds and wouldn't be around to use them, they were very eager to get those funds," he said.
To date, investigators have not unearthed evidence that Hasan sent money to charities with strong or suspected ties to Islamist militant groups, but they are continuing to probe his financial dealings as one aspect of a many-pronged case, other sources cautioned.
The FBI obtained the e-mails pursuant to court-ordered wiretaps, according to a former intelligence official. After receiving a wiretap order, Internet providers generally set up accounts that allow cloned copies of e-mails to go to the government agency in real time. Stored e-mails also may be provided with a search warrant.
In this case, a first batch of Hasan's e-mails was sent by agents in San Diego to the bureau's Washington field office, where a terrorism task force began to assess them in December. But months later, additional messages emerged, according to government and congressional sources. Those e-mails were reviewed only in San Diego, where authorities determined they did not pose a national security risk. The FBI said last week, without going into details about the process, that "all of the e-mails were known."
Hasan's commanding officer ordered him to "pre-trial confinement" on Friday, John Galligan, the suspect's attorney, said in an interview at his Belton, Tex., office. Galligan described pre-trial confinement as the strictest confinement in military court and said it usually means the suspect is locked in a military jail. Because Hasan is paralyzed and has substantial medical needs, Galligan said he will ask for his client to remain in intensive care under guarded supervision.
"He's in a hospital bed," Galligan said. "He's not going to get up and walk away."
In several of their applications for search warrants, authorities are approaching the matter as a regular criminal investigation rather than invoking special legal authority available in terrorism cases, the sources said.
What, if anything, authorities on the task force and in the Army should have done differently after Hasan emerged as a possible problem is the subject of multiple congressional and executive branch investigations, including one ordered by President Obama.
At a congressional hearing Thursday, Sen. Joseph I. Lieberman (I-Conn.), chairman of the Homeland Security and Governmental Affairs Committee, said that Hasan had conducted a "homegrown terrorist attack" -- a conclusion investigators have yet to reach.
But several current and former investigators who handle high-profile cases said that not citing terrorism as a possible motivation for Hasan at this stage may be a function of the legal standards imposed by prosecutors preparing the search applications.
Investigators within the FBI and the Defense Department continue to operate on the theory that Hasan acted alone, though they have demonstrated interest in his relationships with other soldiers including Duane Reasoner Jr., a convert to Islam who dined with Hasan at a local restaurant in the months before the attack.